The invention relates to transmission of digital information, and in particular, to receivers and decoding methods for digital information transmission.
FIG. 1 illustrates a generic digital communications system (such as mobile, satellite, wireline, TV broadcast, air traffic control, car-phone, PCS, and so forth) for transmission of digital information (such as speech, audio, video, data, and so forth) from a digital information source via an encoder and a data channel to a digital information sink which is preceded by a decoder in which the data transmitted by the information source are equalized and decoded (reconstructed) and where the most-likely-transmitted data sequence is forwarded to the information sink. Typically, non-ideal characteristics of the data channel lead to intersymbol interference (ISI) of the transmitted symbols. The optimum receiver for ISI channels in terms of error event probability is the maximum likelihood sequence estimator (NESE) implemented with the Viterbi Algorithm (VA); see for example, Lou, Implementing the Viterbi Algorithm, IEEE Signal Processing Mag. 42-52 (September 1995).
Since the complexity of the VA grows exponentially with the length of the channel impulse response, a number of methods have been proposed to achieve the performance of the VA with reduced complexity. These methods are based on one of the following approaches: (1) consider only a fixed number of most likely state sequences of the VA at each symbol interval: (2) truncate the length of the channel impulse response by a prefilter such as with decision feedback sequence estimation; (3) use the idea of set partitioning known from trellis coded modulation; and (4) at each time step only extend those paths whose path metric differs from the smallest path metric by less than an arbitrarily chosen constant.
However, more effective methods are needed.
The present invention provides a reduced complexity Viterbi type decoding method and receiver by discarding paths whose metrics differ from a smallest metric by more than a constant related to the minimum distance between paths.
This has advantages including reduction in the complexity of the Viterbi type decoder with estimable